Heat induces the transversion G:C yields C:G in bacteriophage T4, and guanylic residues are the target bases. We have proposed that the mutagenic product is deoxyneoguanosine (deoxyguanosine with the glycosidic linkage transferred to the guanine N2). We will synthesize deoxyneoguanosine triphosphate and incorporate it into defined oligodeoxynucleotides suitable for determining which progeny bases are templated by this novel pyrimidine analogue, and whether there exist repair enzymes capable of excising this base. BIBLIOGRAPHIC REFERENCES: Drake, J.W. (1977) Mutagenic mechanisms in bacteriophage T4. Stadler Symp. 8, in press. Williams, W.E. and J.W. Drake (1977) Mutator mutations in bacteriophage T4 gene 42 (dCMP hydroxymethylase). Genetics, in press.